Preparation of Highly Luminescent Nanocrystals and Their Application to Light‐Emitting Diodes

Lim, Jae Yol; Jun, Sangmi; Jang, Eunjoo; Baik, Hionsuck; Kim, Hyungkun; Cho, Jaehee

doi:10.1002/adma.200602642

Cited by 221 publications

(172 citation statements)

References 31 publications

Supporting

Mentioning

170

Contrasting

Order By: Relevance

“…30 The diameter of the CdSe QDs was estimated from a sizing curve relating the first exciton peak energy with the nanocrystal size. 15 High-quality CdSe/ CdS/ZnS coreÀshellÀshell QDs were prepared according to the one-pot multistage method reported by Lim et al 26 The core diameter was 3.4 nm, and after overcoating with about 3 monolayers of CdS and 2 monolayers of ZnS, the particle size increased to 7 nm. CdSe/CdS dot core/rod shell nanorods were synthesized following the procedure described by Manna et al, 42 using CdSe QDs with 3.2 nm diameter seeds.…”

Section: Methodsmentioning

confidence: 99%

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

et al. 2012

View full text Add to dashboard Cite

A high luminescence efficiency is an important property of colloidal quantum dots (QDs), and quantum yields higher than 90% have been reported for coreÀshell QDs. 1 High efficiencies are especially important for application of QDs as luminescent biolabels, 2 in QD lasers, 3 in spectral converters for warm white LEDs, 4,5 electroluminescent devices, 6 and solar concentrators. 7 Luminescence efficiencies are strongly temperature-dependent. 8 Extensive temperature-dependent luminescence studies for colloidal QDs have been conducted at cryogenic temperatures (0.3À300 K). 9À15 In this temperature region, interesting effects were observed, including a prolonged lifetime below 20 K related to brightÀdark state splitting, 11,16 thermally activated quenching due to surface defect states, 9,10,17 and temperature antiquenching assigned to a phase transition in the capping layer. 14,15 However, the luminescence properties of QDs above room temperature (RT) are hardly investigated, and yet, for most applications in luminescent devices, the working temperature is higher than 300 K. An interesting example is the recent application of QDs as color converters in warm-white LEDs, 18 in which QDs serve as narrow band red emitters under excitation with blue light from a (In,Ga)N LED. The narrow emission bandwidth renders QDs superior to classical phosphors based on broad band emission from luminescent ions. 19 In high-power LEDs for general lighting applications, the heat generated in the pÀn junction and phosphor converter layer leads to temperatures as high as 150À200°C in the layer applied on top of the blue diode. 20 To avoid these high temperatures, the QD phosphor layer can be placed in a more remote configuration. Still, temperatures in such a configuration are expected to be well above 50°C due to heat dissipation of the QDs themselves (excess energy from converting the blue into red light). Clearly, the quenching of QD luminescence at elevated temperatures is relevant for application of QDs in luminescent devices, and a better insight in the quenching behavior is needed.Despite its importance, research on luminescence temperature quenching above RT is very limited for QDs. It is theoretically expected for a QD to have a very high luminescence quenching temperature (T q ). Three generally accepted mechanisms for thermal quenching involve thermally activated crossover from the excited state to the ground state, multiphonon relaxation, and thermally activated photoionization. The first mechanism is generally depicted in a simple configurational coordinate diagram. 8,21 The energy difference between the minimum * Address correspondence to a.meijerink@uu.nl.Received for review July 18, 2012 and accepted September 14, 2012. Published online 10.1021/nn303217qABSTRACT Thermal quenching of quantum dot (QD) luminescence is important for application in luminescent devices. Systematic studies of the quenching behavior above 300 K are, however, lacking. Here, high-temperature (300À500 K) luminescence studies are reported for highly ef...

show abstract

Section: Methodsmentioning

confidence: 99%

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

et al. 2012

View full text Add to dashboard Cite

show abstract

“…[5][6][7][8] Recently, several studies were conducted to elucidate quantum dot (QD) formation, [9][10][11] specifically the mechanisms underlying the generation of monomers [12][13][14] from various metal and chalocogenide precursors. Almost all previous studies have exclusively used trialkylphosphine chalcogenides (R3P=E; E= S, Se, Te) for the production of metal chalocogenide QDs, and from spectroscopic analysis it was proposed that "magic-sized" nanocrystals (MSNs) (<1.5 nm in diameter) are formed as key intermediates, which undergo further growth to form QDs.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

Dolai¹,

Dutta

Muhoberac³

et al. 2015

Chem. Mater.

View full text Add to dashboard Cite

ABSTRACT:We have designed a new non-phosphinated reaction pathway, which includes synthesis of a new, highly reactive Se-bridged organic species (chalcogenide precursor), to produce bright white light-emitting ultrasmall CdSe nanocrystals of high quality under mild reaction conditions. The detailed characterization of structural properties of the selenium precursor through combined 77 Se NMR and laser desorption ionization-mass spectrometry (LDI-MS) provided valuable insights into Se release and delineated the nanocrystal formation mechanism at the molecular level. The 1 H NMR study showed that the rate of disappearance of Se-precursor maintained a single-exponential decay with a rate constant of 2.3 x 10 -4 s -1 at room temperature. Furthermore, the combination of LDI-MS and optical spectroscopy was used for the first time to deconvolute the formation mechanism of our bright white light-emitting nanocrystals, which demonstrated initial formation of a smaller key nanocrystal intermediate (CdSe)19. Application of thermal driving force for destabilization resulted in (CdSe)n nanocrystal generation with n = 29-36 through continuous dissolution and addition of monomer onto existing nanocrystals while maintaining a living-polymerization type growth mode. Importantly, our ultrasmall CdSe nanocrystals displayed an unprecedentedly large fluorescence quantum yield of ~27% for this size regime (<2.0 nm diameter). These mixed oleylamine and cadmium benzoate ligand-coated CdSe nanocrystals showed a fluorescence lifetime of ~90 ns, a significantly large value for such small nanocrystals, which was due to delocalization of the exciton wavefunction into the ligand monolayer. We believe our findings will be relevant to formation of other metal chalcogenide nanocrystals through expansion of the understanding and manipulation of surface ligand chemistry, which together will allow the preparation of "artificial solids" with high charge conductivity and mobility for advanced solid-state device applications.3

show abstract

“…5 also shows the photographs of the red, green, blue, yellow, and orange monochromatic QD-LEDs operated at 100 mA. The peak wavelength of the monochromatic QD-LEDs demonstrates a slight red shift and broadened bandwidth, which can be attributed to the CdSe QD aggregation inside the PMMA resin [37]. Apart from single color devices, appropriately mixed QDs can generate white light at different CCTs.…”

Section: Resultsmentioning

confidence: 99%

Wide-Range Correlated Color Temperature Light Generation From Resonant Cavity Hybrid Quantum Dot Light-Emitting Diodes

Chen

Lin

Han

et al. 2015

IEEE J. Select. Topics Quantum Electron.

View full text Add to dashboard Cite

Abstract-This study presents extremely uniform colloidal quantum dot white light-emitting diodes (QD-WLEDs) that demonstrate a high color rendering index (CRI) and correlated color temperatures (CCTs) ranging from 2500 to 4500 K. Experimental results indicate that the structure of the distributed Bragg reflector (DBR) containing a stopband in the UV region enhances the intensity output of both monochromatic QD-LEDs and QD-WLEDs by reflecting the unconverted UV light back onto the package to excite the QDs further. Furthermore, the angular CCT uniformity of the QD-WLEDs also improved considerably because of the dependence of the DBR structure on the incident angle. The angular CCT deviation in the range of -70°to 70°de-creased to 39 K and the CRI of the WLED is higher than 90. The high-CRI and uniform angular CCT QD-WLED containing the DBR demonstrates potential applicability as the lighting source of next-generation display devices and solid-state lighting.

show abstract

Preparation of Highly Luminescent Nanocrystals and Their Application to Light‐Emitting Diodes

Cited by 221 publications

References 31 publications

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

Wide-Range Correlated Color Temperature Light Generation From Resonant Cavity Hybrid Quantum Dot Light-Emitting Diodes

Contact Info

Product

Resources

About